Adds anonymous functions to AILang. A lambda value is constructed by
malloc'ing an env struct that holds its captured locals, plus a
closure pair `{ thunk_ptr, env_ptr }` (Iter 8a's ABI). The lambda's
body lifts to a top-level thunk `@ail_<m>_<def>_lam<id>(ptr %env,
params...)` that unpacks captures back into named locals before
running.
AST: new Term::Lam { params, paramTypes, retType, effects, body }.
Serde tag is "lam"; existing modules (no Lam) serialize identically,
so all current hashes stay stable.
Pretty-printer: renders `(\\ (x: T ...) -> R . body)`.
Typecheck (ailang-check): a lambda's type is the declared Type::Fn.
Body's effect set must be a subset of declared effects (no row
polymorphism). Constructing a lambda is pure — only calling it picks
up the declared effects, via the existing App branch.
Codegen (ailang-codegen):
- collect_captures: free-var walk; excludes builtins, current-module
top-level fns, and qualified names.
- lower_lambda: per-fn lam counter, save/restore emitter state, emit
thunk into a deferred queue (flushed after the parent fn), pack env
+ closure pair on heap, register the resulting closure-pair SSA in
the sidetable so subsequent indirect calls find it.
- Capture sigs propagate: a fn-typed capture keeps its FnSig in the
thunk's sidetable so `f(args)` inside the body still indirect-calls.
- Env layout: 8 bytes per capture (typed load/store reads only the
needed bytes; padding wasted but uniform).
Tests: 49 green (was 48). New examples/closure.ail.json + e2e
`closure_captures_let_n` exercises `let n = 3 in apply(\\x. x + n, 39)`
end-to-end and asserts the binary prints 42.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
